Difficulty understanding how to declare a parent class's function in an extended class?

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Classes in Java exist in a hierarchy. A class in Java can be declared as a subclass of another class using the extends keyword. A subclass inherits variables and methods from its superclass and can use them as if they were declared within the subclass itself:,In Java, a class that contains one or more abstract methods must be explicitly declared as an abstract class, also using the abstract modifier:,A subclass can be further subclassed. Normally, subclassing specializes or refines a class by adding variables and methods (you cannot remove or hide variables or methods by subclassing). For example:,Inside of DecimalCalculator, the super keyword used in this manner selects the sum variable defined in the superclass. We’ll explain the use of super more fully in a bit.

    class IntegerCalculator {
       int sum;
       ...
    }

    class DecimalCalculator extends IntegerCalculator {
       double sum;
       ...
    }
    int s = super.sum;
    DecimalCalculator dc = new DecimalCalculator();
    IntegerCalculator ic = dc;

    int s = ic.sum; // accesses IntegerCalculator sum
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The syntax to extend another class is: class Child extends Parent.,Let’s create class Rabbit that inherits from Animal:,Class inheritance is a way for one class to extend another class.,To extend a class: class Child extends Parent: That means Child.prototype.__proto__ will be Parent.prototype, so methods are inherited.

class Animal {
   constructor(name) {
      this.speed = 0;
      this.name = name;
   }
   run(speed) {
      this.speed = speed;
      alert(`${this.name} runs with speed ${this.speed}.`);
   }
   stop() {
      this.speed = 0;
      alert(`${this.name} stands still.`);
   }
}

let animal = new Animal("My animal");
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If we try to use the live_with_anemone() method in a Trout object, we’ll receive an error:,We can now create a Trout object without having to define any additional methods.,The output shows that the Clownfish object casey is able to use the Fish methods __init__() and swim() as well as its child class method of live_with_anemone().,This is because the method live_with_anemone() belongs only to the Clownfish child class, and not the Fish parent class.

class Fish:
   def __init__(self, first_name, last_name = "Fish"):
   self.first_name = first_name
self.last_name = last_name
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To declare inheritance in Java, we simply add extends [superclass] after the subclass’s identifier.,Java inheritance examples,final Class cannot be a parent class for any subclass,There are several types of inheritance available in Java:

Subclasses are linked to superclasses using the extends keyword during their definition. Subclasses can define new local methods or fields to use or can use the super keyword to call inherited methods or the super constructor.

class b {
   // implementation of inheritedMethod()
}
class a extends b {
   inheritedMethod();
}
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In order to understand this, let us consider the example below where we declare a variable x with the same name in both Parent and Child classes.,When we declare a variable in a Child class, which has the same name, e.g. x as an instance variable in a Parent class, then:,When we create a variable in both parent and child classes with the same name and try to access it using a parent's class reference, which is holding a child class's object, then what do we get?,The Child class's object contains both variables (one inherited from the Parent class and another declared in Child itself) but the child class variable hides the parent class's variable.

In order to understand this, let us consider the example below where we declare a variable x with the same name in both Parent and Child classes.

class Parent {
   // Declaring instance variable by name `x`
   String x = "Parent`s Instance Variable";

   public void print() {
      System.out.println(x);
   }
}

class Child extends Parent {

   // Hiding Parent class's variable `x` by defining a variable in child class with same name.
   String x = "Child`s Instance Variable";

   @Override
   public void print() {
      System.out.print(x);

      // If we still want to access variable from super class, we do that by using `super.x`
      System.out.print(", " + super.x + "\n");
   }
}
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Arrays.sort() in Java with examples,Split() String method in Java with examples,The reference variable of the Parent class is capable to hold its object reference as well as its child object reference.In Java, methods are virtual by default (See this for details).What about non-method members. For example, predict the output of following Java program. ,HashMap in Java with Examples

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The extends keyword is used in class declarations or class expressions to create a class that is a child of another class. , The extends keyword can be used to subclass custom classes as well as built-in objects. , Classes Class static initialization blocksconstructorextendsPrivate class featuresPublic class fieldsstatic , The first example creates a class called Square from a class called Polygon. This example is extracted from this live demo (source).

class ChildClass extends ParentClass {
   ...
}
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Let's understand the problem that we may face in the program if we don't use method overriding.,Understanding the problem without method overriding,The method must have the same name as in the parent class,Let's see the concept of method overriding with exception handling.

Vehicle is running
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Unless autoloading is used, the classes must be defined before they are used. If a class extends another, then the parent class must be declared before the child class structure. This rule applies to classes that inherit other classes and interfaces. , For example, when extending a class, the subclass inherits all of the public and protected methods, properties and constants from the parent class. Unless a class overrides those methods, they will retain their original functionality. , This is useful for defining and abstracting functionality, and permits the implementation of additional functionality in similar objects without the need to reimplement all of the shared functionality. , The visibility of methods, properties and constants can be relaxed, e.g. a protected method can be marked as public, but they cannot be restricted, e.g. marking a public property as private.

This is useful for defining and abstracting functionality, and permits the implementation of additional functionality in similar objects without the need to reimplement all of the shared functionality.

Private methods of a parent class are not accessible to a child class. As a result, child classes may reimplement a private method themselves without regard for normal inheritance rules. Prior to PHP 8.0.0, however, final and static restrictions were applied to private methods. As of PHP 8.0.0, the only private method restriction that is enforced is private final constructors, as that is a common way to "disable" the constructor when using static factory methods instead.

final

This is useful for defining and abstracting functionality, and permits the implementation of additional functionality in similar objects without the need to reimplement all of the shared functionality.

Private methods of a parent class are not accessible to a child class. As a result, child classes may reimplement a private method themselves without regard for normal inheritance rules. Prior to PHP 8.0.0, however, final and static restrictions were applied to private methods. As of PHP 8.0.0, the only private method restriction that is enforced is private final constructors, as that is a common way to "disable" the constructor when using static factory methods instead.

static

This is useful for defining and abstracting functionality, and permits the implementation of additional functionality in similar objects without the need to reimplement all of the shared functionality.

Private methods of a parent class are not accessible to a child class. As a result, child classes may reimplement a private method themselves without regard for normal inheritance rules. Prior to PHP 8.0.0, however, final and static restrictions were applied to private methods. As of PHP 8.0.0, the only private method restriction that is enforced is private final constructors, as that is a common way to "disable" the constructor when using static factory methods instead.

private final
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